1. Field of the Invention
The present invention relates to a pressure generator and, more particularly, to a dispensing apparatus utilizing such a pressure generator for dispensing product from sealed containers.
2. Description of the Prior Art
Aerosol pressurized dispensers have become familiar, if not essential, products in both consumer and industrial use due to the efficient way in which they discharge a myriad of products.
A common example is the hair spray dispenser in which, inside the dispenser, the product spray is dispersed in and surrounded by a liquefied propellant gas under pressure forming a uniform, single phase mixture of the product spray and the liquefied propellant. As the product release valve is pressed, the liquefied propellant immediately vaporizes forcing the product spray out of the dispenser in the form of a fine mist.
A second type of aerosol dispenser, the cheese spread dispenser being a common example, discharges the product, not as a fine mist, but as a solid. In this second category of aerosol dispensers, the propellant exists within the dispenser as a gas and does not mix with the product. Rather, it forms a separate layer over the product to be discharged. As the product release valve is pressed, the propellant, being under pressure, pushes the product out of the dispenser.
The most commonly used propellants are butane, nitrogen and chlorinated fluorohydrocarbons (CFC's), such as those sold under trade name of Freon. CFC's and butane are often preferred over nitrogen since their vapor pressures are independent of the volume of free headspace in the dispenser. Thus, as long as some of the CFC or butane is present in the dispenser, the pressure exerted on the product is virtually constant throughout the discharge life of the system.
However, both CFC's and butane have adverse effects on the environment. CFC's add to the destruction of the earth's protective ozone layer which has lead the world community to seek a complete ban of CFC usage. Many countries have already banned its use or have implemented programs and schedules designed to eliminate CFC usage in the near future. Butane, on the other hand, is extremely flammable, making storage, handling and use of butane charged containers very hazardous. In addition, butane contaminates the flavor and smell of the dispensed product, thereby further restricting its use.
Although nitrogen is available as a substitute propellant, its vapor pressure is such that as product is dispensed, the propellant pressure decreases. Therefore, the product cannot be dispensed at a constant pressure through the life of the product, and at some point, the propellant pressure will fall below that needed to propel any product from the dispenser. To enable all of the product to be dispensable, the nitrogen must be pressurized to dangerously high levels increasing the risk of rupture or requiring more costly dispenser construction.